Free-standing $AlxGa1−xAs$ heterostructures by gas-phase etching of germanium

We outline a facile fabrication technique for the realization of free-standing $AlxGa1−xAs$ heterostructures of arbitrary aluminum content. Utilizing xenon difluoride $(XeF2)$ we rapidly and selectively remove a sacrificial germanium (Ge) underlayer in a room temperature gas-phase etching procedure. We demonstrate two possibilities for exploiting this unique process: (1) bulk micromachining of a suspended high-frequency low-dissipation micro-optomechanical resonator consisting of an epitaxial GaAs/AlAs multilayer grown on a Ge substrate and (2) epitaxial lift-off of a GaAs film via removal of an embedded Ge sacrificial layer, resulting in lateral etch rates up to 3 mm/h and a conservative selectivity of $∼106$⁠.